1. Field of the Invention
The present invention relates to an electronic alarm system for a motor vehicle, and more particularly to an electronic alarm system that it is fully automatic and ignition operated.
2. Description of the Prior Art
The prior art includes many antitheft circuits which operate by grounding the ignition system of the motor vehicle, severing its fuel supply, or sounding a alarm such as a horn or a siren. Most of these antitheft circuits include control switches that are hidden within the operator's compartment of the motor vehicle so that a would be thief is foiled in his attempt to enter the motor vehicle or having once entered the motor vehicle in his attempt to find the antitheft circuit and to disable it. When the antitheft circuit is made standard equipment on a motor vehicle, it will be placed in a standard position within the operator's compartment. This will enable the would be thief to find the antitheft circuit and to disable it. Furthermore, these control switches must be activated every time the operator leaves the motor vehicle unattended.
U.S. Pat. No. 3,585,584, entitled Intruder Detector and Warning System, issued to Gene E. Behread on June 15, 1971, teaches a transistorized circuit adapted to be employed in a motor vehicle and set so that it will respond whenever a would be thief opens the hood or any door of the motor vehicle and will effect the activation of an alarm. When the would be thief opens the hood or any door of the motor vehicle, the transistorized circuit will disable the ignition circuit. The transistorized circuit provides a delay in the setting in order to accommodate the operator's exiting from the motor vehicle and then responds to any subsequent opening of the hood or any door of the motor vehicle whenever the ignition switch is in the off position. The transistorized circuit operates in conjunction with an alarm, which is generally a horn or a siren, an alarm relay which is electrically coupled to the alarm and which is triggered by the transistorized circuit, a 12 volt power source, the ignition switch of the motor vehicle which is electrically coupled to a set circuit of the transistorized circuit, and a combination of a hood switch and door switches electrically coupled to a detector control of the transistorized circuit to form an intruder detector and warning system.
The transistorized circuit includes a set circuit which is electrically coupled to the ignition switch and which turns the transistorized circuit on, a detector control which is electrically coupled to the hood switch and the door switches, a time delay circuit which is electrically coupled to the set circuit and to the detector control, a time on circuit which is electrically coupled to the detector control, a reset delay circuit which is electrically coupled to the time on circuit, and a multivibrator circuit which is electrically coupled to the reset delay circuit and which triggers the alarm relay thereby sounding the alarm. Each of these circuits contain many discrete components and the cost of these components and the cost of assembling these component is expensive. Furthermore, the transistorized circuit is relatively large and cumbersome so that it can not be easily hidden from plain view.
U.S. Pat. No. 3,643,214, entitled Solid-State Burglar Alarm System For Automobile, issued to Ronald E. Chan on Feb. 15, 1972, teaches a solid state burglar alarm system for operation with the courtesy light circuit of an automobile. The alarm system includes a main switch hidden within the operator's compartment of the automobile for energizing or de-energizing the alarm system and also includes an exit timer so that the operator can exit the automobile without triggering the alarm system. The alarm system consists of many discrete solid state components such as diodes, transistors, silicon controlled rectifiers (SCRs) and field effect transistors (FETs). These components are not only costly to buy, but also costly to assemble into the alarm system. Additionally it is a disadvantage of this alarm system that it must rely on a hidden switch to energize or de-energize itself.
U.S. Pat. No. 3,649,962, entitled Vehicle Alarm System, issued to Peter R. Bedard and Charles J. Spall, Jr. on Mar. 14, 1972 teaches a vehicle alarm system which includes a thermostatic delay relay which consists of a heater resistor and an armature which reacts to the heat from the heater resistor and closes after a particular period of delay thereby triggering an alarm. A set of tampering switches provide the current to the heater resistor whenever the motor vehicle is being tampered with by a would be thief. The problem with this alarm system is that the delay time can not be varied to suit the individual preferences of each operator of the motor vehicle.